Question: Simplify the following expression: $r = \dfrac{a}{2} + \dfrac{9a}{8}$
Explanation: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $2$ and $8$ $\lcm(2, 8) = 8$ $ r = \dfrac{4}{4} \cdot \dfrac{a}{2} + \dfrac{1}{1} \cdot \dfrac{9a}{8} $ $r = \dfrac{4a}{8} + \dfrac{9a}{8}$ $r = \dfrac{4a +9a}{8}$ $r = \dfrac{13a}{8}$